ome of the other organisms that are known to be pyogenic, such as the
bacillus pyocyaneus, which is found in green and blue pus, the
micrococcus tetragenus, the gonococcus, actinomyces, the glanders
bacillus, and the tubercle bacillus. Most of these will receive further
mention in connection with the diseases to which they give rise.

#Leucocytosis.#--Most bacterial diseases, as well as certain other
pathological conditions, are associated with an increase in the number
of leucocytes in the blood throughout the circulatory system. This
condition of the blood, which is known as _leucocytosis_, is believed to
be due to an excessive output and rapid formation of leucocytes by the
bone marrow, and it probably has as its object the arrest and
destruction of the invading organisms or toxins. To increase the
resisting power of the system to pathogenic organisms, an artificial
leucocytosis may be induced by subcutaneous injection of a solution of
nucleinate of soda (16 minims of a 5 per cent. solution).

The _normal_ number of leucocytes per cubic millimetre varies in
different individuals, and in the same individual under different
conditions, from 5000 to 10,000: 7500 is a normal average, and anything
above 12,000 is considered abnormal. When leucocytosis is present, the
number may range from 12,000 to 30,000 or even higher; 40,000 is looked
upon as a high degree of leucocytosis. According to Ehrlich, the
following may be taken as the standard proportion of the various forms
of leucocytes in normal blood: polynuclear neutrophile leucocytes, 70 to
72 per cent.; lymphocytes, 22 to 25 per cent.; eosinophile cells, 2 to 4
per cent.; large mononuclear and transitional leucocytes, 2 to 4 per
cent.; mast-cells, 0.5 to 2 per cent.

In estimating the clinical importance of a leucocytosis, it is not
sufficient merely to count the aggregate number of leucocytes present. A
differential count must be made to determine which variety of cells is
in excess. In the majority of surgical affections it is chiefly the
granular polymorpho-nuclear neutrophile leucocytes that are in excess
(_ordinary leucocytosis_). In some cases, and particularly in parasitic
diseases such as trichiniasis and hydatid disease, the eosinophile
leucocytes also show a proportionate increase (_eosinophilia_). The term
_lymphocytosis_ is applied when there is an increase in the number of
circulating lymphocytes, as occurs, for example, in lymphatic leucaemia,
and in ce